Effect of moisture content on characteristic stress and acoustic emission characteristics of red sandstone

In order to investigate the response law of moisture content to the characteristic stress and acoustic emission characteristics of red sandstone, the uniaxial compression tests of red sandstone under different moisture content conditions were conducted using RMT-150C rock mechanical pressure testing machine and PCI-Ⅱ AE win acoustic emission system. The physical and mechanical parameters and characteristic stress evolution mechanism of red sandstone under water erosion are analyzed, and the evolution law of acoustic emission (wide and narrow-band) time series mode under different moisture content conditions is also investigated. At the same time, the damage evolution model of red sandstone is constructed based on cumulative acoustic emission event number and statistical mechanics theory. The results show that: 1) The P-wave velocity decreases first and then increases with the increase of moisture content. When the water saturation reaches a critical value, the P-wave velocity will drop to the lowest value. 2) The acoustic emission signal received by the narrow-band receiving sensor is closely related to the friction between the particles in the red sandstone, and the acoustic emission signal received by the wide-band receiving sensor is intrinsically related to the evolution of the internal cracks in the red sandstone. 3) The moisture content has a significant effect on the acoustic emission event rate (wide-band) at the stage of unstable crack propagation, and has a minor effect on the ratio of characteristic stress to peak strength, but it has a relatively obvious effect on the strain percentage at each stage. With the increase of moisture content, the failure mode of red sandstone specimens gradually changes from brittle failure to ductile failure. 4) As the moisture content increases, a "backward" change trend can be observed for the active period of acoustic emission event rate (narrow-band), and the acoustic emission modes of dry, natural, and saturated rock samples correspond to mass shocks, pre-main-later shocks and swarm shocks type, respectively. (5) According to the damage model based on the cumulative number of acoustic emission events (wide and narrow-band), the damage process of red sandstone can be divided into four stages: initial damage stage, stable damage development stage, accelerated damage development stage and damage destruction stage.